1. Field of the Invention
The present invention relates to a process for converting hydrogen sulfide which is contained in a gaseous feed stream to elemental sulfur and hydrogen by initially reacting hydrogen sulfide with an anthraquinone which is dissolved in a polar organic solvent wherein a relatively small quantity of water is added to the polar organic solvent thereby increasing the elemental sulfur which is recovered, and more particularly, to such a process wherein the relatively small quantity of water which is added to the solvent during the initial reaction stage also increases hydrogen product selectivity in the subsequent dehydrogenation of anthrahydroquinone which is formed in the initial reaction.
2. Description of Related Art
Many processes relating to the petroleum industry generate gaseous by-products containing hydrogen sulfide, either alone or in a mixture with other gases, for example, methane, carbon dioxide, nitrogen, etc. For many years, these gaseous by-products were oxidized by common oxidation processes, such as, the Claus process, to obtain sulfur. In accordance with the Claus process, hydrogen sulfide is oxidized by direct contact with air to produce sulfur and water. However, several disadvantages of air oxidation of hydrogen sulfide, including loss of a valuable hydrogen source, precise air rate control, removal of trace sulfur compounds from spent air, and an upper limit on the ratio of carbon dioxide to hydrogen sulfide, led to the development of alternative processes for the conversion of hydrogen sulfide in gaseous by-products to sulfur.
As detailed in U.S. Pat. No. 4,592,905 to Plummer et al., one such alternative process involves contacting within a reactor a feed gas containing hydrogen sulfide with an anthraquinone which is dissolved in a polar organic solvent. This polar organic solvent preferably has a polarity greater than about 3 Debye units. The resulting reaction between hydrogen sulfide and anthraquinone yields sulfur and the corresponding anthrahydroquinone. The sulfur formed from the reaction between hydrogen sulfide and anthraquinone precipitates from the solution in crystalline form (S.sub.8) and is recovered as a product. However, the polymerization and precipitation of the sulfur formed as S.sub.8 has remained a limiting factor in this process. The amount of sulfur recoverable as an S.sub.8 product has been an unacceptable percentage of the total sulfur formed and the time required to precipitate S.sub.8 as a product is sufficiently long to impede the commercial viability of the process.
The remaining solution containing anthrahydroquinone is thermally or catalytically regenerated thereby producing the initial anthraquinone form and releasing hydrogen gas. The anthraquinone is recycled back to the reactor and the hydrogen gas is recovered as a product. Regeneration or dehydrogenation of anthrahydroquinone using metal supported catalysts causes hydrogenolysis which results in the undesirable production of water and anthrones and/or anthranols. Thus, a need exists for such a process wherein the amount of sulfur which can be precipitated from solution in crystalline form (S.sub.8) and recovered as a product is increased. A further need exists to increase the selectivity of anthrahydroquinone to anthraquinone and hydrogen product in such a process, and thus, decrease unwanted hydrogenolysis by-products, such as anthrones and/or anthranols.
Accordingly, it is an object of the present invention to provide a process for increasing the amount of sulfur obtained from the reaction between hydrogen sulfide and anthraquinone which can be precipitated from solution in crystalline form (S.sub.8) and recovered as a product.
It is a further object of the present invention to provide a process for increasing hydrogen production selectivity during dehydrogenation of anthrahydroquinone, and thus, decrease unwanted hydrogenolysis by-products.
It is a still further object of the present invention to provide a process wherein sulfur which is formed by the reaction between hydrogen sulfide and anthraquinone can be precipitated from solution in crystalline form (S.sub.8) in a commercially acceptable time.